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A glass capillary tube is dipped vertically into a liquid. A student measures the pressure just below the meniscus inside the capillary tube and finds it to be greater than the atmospheric pressure outside. Identify the correct combination of the liquid's meniscus shape, contact angle ( ), and capillary behavior.

Options

  1. AConcave meniscus, < 90^ , and capillary rise.
  2. BConvex meniscus, > 90^ , and capillary rise.
  3. CConcave meniscus, > 90^ , and capillary fall.
  4. DConvex meniscus, > 90^ , and capillary fall.

Correct answer

D. Convex meniscus, > 90^ , and capillary fall.

Step-by-step solution

The pressure on the concave side of a curved liquid surface is always greater than the pressure on the convex side. Since the pressure just below the meniscus is greater than the atmospheric pressure (which is the pressure just above the meniscus), the concave side of the meniscus must be facing downwards. This means the meniscus is convex upwards. A convex meniscus is formed when the cohesive forces are stronger than the adhesive forces, which corresponds to an obtuse contact angle ( > 90^ ). For > 90^ , is negati

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